Composite polyamide membrane having high acid content and low azo content

ABSTRACT

A thin film composite polyamide membrane comprising a porous support and a thin film polyamide layer characterized by possessing: i) an azo (—N═N—) content of from 0.30% to 0.80%, as measured by pyrolysis gas chromatography; and ii) a dissociated carboxylate content of at least 0.18 mol/kg as measured by RBS at pH 9.5.

FIELD

The present invention is generally directed toward composite polyamidemembranes along with methods for making and using the same.

INTRODUCTION

Composite polyamide membranes are used in a variety of fluidseparations. One common class of membranes includes a porous supportcoated with a “thin film” polyamide layer. This class of membrane iscommonly referred to as thin film composite (TFC). The thin film layermay be formed by an interfacial polycondensation reaction betweenpolyfunctional amine (e.g. m-phenylenediamine) and polyfunctional acylhalide (e.g. trimesoyl chloride) monomers which are sequentially coatedupon the support from immiscible solutions, see for example U.S. Pat.No. 4,277,344 to Cadotte. U.S. Pat. No. 4,812,270 and U.S. Pat. No.4,888,116 to Cadotte describe the post-treatment of such membranes withphosphoric or nitrous acid. (See also US2014/0231338, US2013/0256215,US2013/0126419, US2012/0305473, US2012/0261332 and US2012/0248027).US2013/0237946, US2013/0287944, US2013/0287945, WO2013/048765 andWO2013/103666 describe the addition of various monomers includingcarboxylic acid and amine-reactive functional groups in combination withthe addition of a tri-hydrocarbyl phosphate compound as described inU.S. Pat. No. 6,878,278 to Mickols. The search continues for newcombinations of monomers, additives and post-treatments that furtherimprove polyamide membrane performance.

SUMMARY

The invention includes a thin film composite polyamide membranecomprising a porous support and a thin film polyamide layercharacterized by possessing:

i) an azo (−N═N−) content of from 0.30% to 0.80%, as measured bypyrolysis gas chromatography; and

ii) a dissociated carboxylate content of at least 0.18 mol/kg asmeasured by RBS at pH 9.5. Many embodiments are described includingapplications for such membranes.

DETAILED DESCRIPTION

The invention is not particularly limited to a specific type,construction or shape of composite membrane or application. For example,the present invention is applicable to flat sheet, tubular and hollowfiber polyamide membranes useful in a variety of applications includingforward osmosis (FO), reverse osmosis (RO), nano filtration (NF), ultrafiltration (UF), micro filtration (MF) and pressure retarded fluidseparations. However, the invention is particularly useful for membranesdesigned for RO and NF separations. RO composite membranes arerelatively impermeable to virtually all dissolved salts and typicallyreject more than about 95% of salts having monovalent ions such assodium chloride. RO composite membranes also typically reject more thanabout 95% of inorganic compounds as well as organic molecules withmolecular weights greater than approximately 100 Daltons. NF compositemembranes are more permeable than RO composite membranes and typicallyreject less than about 95% of salts having monovalent ions whilerejecting more than about 50% (and often more than 90%) of salts havingdivalent ions—depending upon the species of divalent ion. NF compositemembranes also typically reject particles in the nanometer range as wellas organic molecules having molecular weights greater than approximately200 to 500 Daltons (AMU).

Examples of composite polyamide membranes include a flat sheet compositemembrane comprising a bottom layer (back side) of a nonwoven backing web(e.g. PET scrim), a middle layer of a porous support having a typicalthickness of about 25-125 μm and top layer (front side) comprising athin film polyamide layer having a thickness typically less than about 1micron, e.g. from 0.01 micron to 1 micron but more commonly from about0.01 to 0.1 μm. The porous support is typically a polymeric materialhaving pore sizes which are of sufficient size to permit essentiallyunrestricted passage of permeate but not large enough so as to interferewith the bridging over of a thin film polyamide layer formed thereon.For example, the pore size of the support preferably ranges from about0.001 to 0.5 μm. Non-limiting examples of porous supports include thosemade of: polysulfone, polyether sulfone, polyimide, polyamide,polyetherimide, polyacrylonitrile, poly(methyl methacrylate),polyethylene, polypropylene, and various halogenated polymers such aspolyvinylidene fluoride. For RO and NF applications, the porous supportprovides strength but offers little resistance to fluid flow due to itsrelatively high porosity.

Due to its relative thinness, the polyamide layer is often described interms of its coating coverage or loading upon the porous support, e.g.from about 2 to 5000 mg of polyamide per square meter surface area ofporous support and more preferably from about 50 to 500 mg/m². Thepolyamide layer is preferably prepared by an interfacialpolycondensation reaction between a polyfunctional amine monomer and apolyfunctional acyl halide monomer upon the surface of the poroussupport as described in U.S. Pat. No. 4,277,344 and U.S. Pat. No.6,878,278. More specifically, the polyamide membrane layer may beprepared by interfacially polymerizing a polyfunctional amine monomerwith a polyfunctional acyl halide monomer, (wherein each term isintended to refer both to the use of a single species or multiplespecies), on at least one surface of a porous support. As used herein,the term “polyamide” refers to a polymer in which amide linkages(—C(O)NH—) occur along the molecular chain. The polyfunctional amine andpolyfunctional acyl halide monomers are most commonly applied to theporous support by way of a coating step from solution, wherein thepolyfunctional amine monomer is typically coated from an aqueous-basedor polar solution and the polyfunctional acyl halide from anorganic-based or non-polar solution. Although the coating steps need notfollow a specific order, the polyfunctional amine monomer is preferablyfirst coated on the porous support followed by the polyfunctional acylhalide. Coating can be accomplished by spraying, film coating, rolling,or through the use of a dip tank among other coating techniques. Excesssolution may be removed from the support by air knife, dryers, ovens andthe like.

The polyfunctional amine monomer comprises at least two primary aminegroups and may be aromatic (e.g., m-phenylenediamine (mPD),p-phenylenediamine, 1,3,5-triaminobenzene, 1,3,4-triaminobenzene,3,5-diaminobenzoic acid, 2,4-diaminotoluene, 2,4-diaminoanisole, andxylylenediamine) or aliphatic (e.g., ethylenediamine, propylenediamine,cyclohexane-1,3-diameine and tris (2-diaminoethyl) amine). Oneparticularly preferred polyfunctional amine is m-phenylene diamine(mPD). The polyfunctional amine monomer may be applied to the poroussupport as a polar solution. The polar solution may contain from about0.1 to about 10 wt % and more preferably from about 1 to about 6 wt %polyfunctional amine monomer. In one set of embodiments, the polarsolutions includes at least 2.5 wt % (e.g. 2.5 to 6 wt %) of thepolyfunctional amine monomer. Once coated on the porous support, excesssolution may be removed.

The polyfunctional acyl halide monomer comprises at least two acylhalide groups and preferably no carboxylic acid functional groups andmay be coated from a non-polar solvent although the polyfunctional acylhalide may be alternatively delivered from a vapor phase (e.g., forpolyfunctional acyl halides having sufficient vapor pressure). Thepolyfunctional acyl halide is not particularly limited and aromatic oralicyclic polyfunctional acyl halides can be used along withcombinations thereof. Non-limiting examples of aromatic polyfunctionalacyl halides include: trimesic acyl chloride, terephthalic acylchloride, isophthalic acyl chloride, biphenyl dicarboxylic acylchloride, and naphthalene dicarboxylic acid dichloride. Non-limitingexamples of alicyclic polyfunctional acyl halides include: cyclopropanetri carboxylic acyl chloride, cyclobutane tetra carboxylic acylchloride, cyclopentane tri carboxylic acyl chloride, cyclopentane tetracarboxylic acyl chloride, cyclohexane tri carboxylic acyl chloride,tetrahydrofuran tetra carboxylic acyl chloride, cyclopentanedicarboxylic acyl chloride, cyclobutane dicarboxylic acyl chloride,cyclohexane dicarboxylic acyl chloride, and tetrahydrofuran dicarboxylicacyl chloride. One preferred polyfunctional acyl halide is trimesoylchloride (TMC). The polyfunctional acyl halide may be dissolved in anon-polar solvent in a range from about 0.01 to 10 wt %, preferably 0.05to 3% wt % and may be delivered as part of a continuous coatingoperation. In one set of embodiments wherein the polyfunctional aminemonomer concentration is less than 3 wt %, the polyfunctional acylhalide is less than 0.3 wt %. Suitable solvents are those which arecapable of dissolving the polyfunctional acyl halide and which areimmiscible with water; e.g. paraffins (e.g. hexane, cyclohexane,heptane, octane, dodecane), isoparaffins (e.g. ISOPAR™ L), aromatics(e.g. Solvesso™ aromatic fluids, Varsol™ non-dearomatized fluids,benzene, alkylated benzene (e.g. toluene, xylene, trimethylbenzeneisomers, diethylbenzene)) and halogenated hydrocarbons (e.g. FREON™series, chlorobenzene, di and trichlorobenzene) or mixtures thereof.Preferred solvents include those which pose little threat to the ozonelayer and which are sufficiently safe in terms of flashpoints andflammability to undergo routine processing without taking specialprecautions. A preferred solvent is ISOPAR™ available from ExxonChemical Company. The non-polar solution may include additionalconstituents including co-solvents, phase transfer agents, solubilizingagents, complexing agents and acid scavengers wherein individualadditives may serve multiple functions. Representative co-solventsinclude: benzene, toluene, xylene, mesitylene, ethyl benzene-diethyleneglycol dimethyl ether, cyclohexanone, ethyl acetate, butyl carbitol™acetate, methyl laurate and acetone. A representative acid scavengerincludes N, N-diisopropylethylamine (DIEA). The non-polar solution mayalso include small quantities of water or other polar additives butpreferably at a concentration below their solubility limit in thenon-polar solution.

One or both of the polar and non-polar solutions additionally includes atri-hydrocarbyl phosphate compound as represented by Formula I.

wherein “P” is phosphorous, “O” is oxygen and R₁, R₂ and R₃ areindependently selected from hydrogen and hydrocarbyl groups comprisingfrom 1 to 10 carbon atoms, with the proviso that no more than one of R₁,R₂ and R₃ are hydrogen. R₁, R₂ and R₃ are preferably independentlyselected from aliphatic and aromatic groups. Applicable aliphatic groupsinclude both branched and unbranched species, e.g. methyl, ethyl,propyl, isopropyl, butyl, isobutyl, pentyl, 2-pentyl, 3-pentyl.Applicable cyclic groups include cyclopentyl and cyclohexyl. Applicablearomatic groups include phenyl and naphthyl groups. Cyclo and aromaticgroups may be linked to the phosphorous atom by way of an aliphaticlinking group, e.g., methyl, ethyl, etc. The aforementioned aliphaticand aromatic groups may be unsubstituted or substituted (e.g.,substituted with methyl, ethyl, propyl, hydroxyl, amide, ether, sulfone,carbonyl, ester, cyanide, nitrile, isocyanate, urethane, beta-hydroxyester, etc); however, unsubstituted alkyl groups having from 3 to 10carbon atoms are preferred. Specific examples of tri-hydrocarbylphosphate compounds include: triethyl phosphate, tripropyl phosphate,tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triphenylphosphate, propyl biphenyl phosphate, dibutyl phenyl phosphate, butyldiethyl phosphate, dibutyl hydrogen phosphate, butyl heptyl hydrogenphosphate and butyl heptyl hexyl phosphate. The specific compoundselected should be at least partially soluble in the solution from whichit is applied. Additional examples of such compounds are described inU.S. Pat. No. 6,878,278, U.S. Pat. No. 6,723,241, U.S. Pat. No.6,562,266 and U.S. Pat. No. 6,337,018.

When combined within the non-polar solution, the solution preferablyincludes from 0.001 to 10 wt % and more preferably from 0.01 to 1 wt %of the tri-hydrocarbyl phosphate compound. In another embodiment, thenon-polar solution includes the tri-hydrocarbyl phosphate compound in amolar (stoichiometric) ratio of 1:5 to 5:1 and more preferably 1:1 to3:1 with the polyfunctional acyl halide monomer. When combined withinthe polar solution, the solution preferably includes from 0.001 to 10 wt% and more preferably from 0.1 to 1 wt % of the tri-hydrocarbylphosphate compound. A preferred species for addition to the polar phaseincludes triethylphosphate.

In a preferred subset of embodiments, the non-polar solution furthercomprises an acid-containing monomer comprising a C₂-C₂₀ hydrocarbonmoiety substituted with at least one carboxylic acid functional group orsalt thereof and at least one amine-reactive functional group selectedfrom: acyl halide, sulfonyl halide and anhydride, wherein theacid-containing monomer is distinct from the polyfunctional acyl halidemonomer. In one set of embodiments, the acid-containing monomercomprises an arene moiety. Non-limiting examples include mono anddi-hydrolyzed counterparts of the aforementioned polyfunctional acylhalide monomers including two to three acyl halide groups and mono, diand tri-hydrolyzed counterparts of the polyfunctional halide monomersthat include at least four amine-reactive moieties. A preferred speciesincludes 3,5-bis(chlorocarbonyl)benzoic acid (i.e. mono-hydrolyzedtrimesoyl chloride or “mhTMC”). Additional examples of monomers aredescribed in WO 2012/102942 and WO 2012/102943 (see Formula III whereinthe amine-reactive groups (“Z”) are selected from acyl halide, sulfonylhalide and anhydride). Specific species including an arene moiety and asingle amine-reactive group include: 3-carboxylbenzoyl chloride,4-carboxylbenzoyl chloride, 4-carboxy phthalic anhydride and 5-carboxyphthalic anhydride, and salts thereof. Additional examples arerepresented by Formula II.

wherein A is selected from: oxygen (e.g. —O—); amino (—N(R)—) wherein Ris selected from a hydrocarbon group having from 1 to 6 carbon atoms,e.g. aryl, cycloalkyl, alkyl-substituted or unsubstituted but preferablyalkyl having from 1 to 3 carbon atoms with or without substituents suchas halogen and carboxyl groups); amide (—C(O)N(R))— with either thecarbon or nitrogen connected to the aromatic ring and wherein R is aspreviously defined; carbonyl (—C(O)—); sulfonyl (—SO₂—); or is notpresent (e.g. as represented in Formula III); n is an integer from 1 to6, or the entire group is an aryl group; Z is an amine reactivefunctional group selected from: acyl halide, sulfonyl halide andanhydride (preferably acyl halide); Z′ is selected from the functionalgroups described by Z along with hydrogen and carboxylic acid. Z and Z′may be independently positioned meta or ortho to the A substituent onthe ring. In one set of embodiments, n is 1 or 2. In yet another set ofembodiments, Z and Z′ are both the same (e.g. both acyl halide groups).In another set of embodiments, A is selected from alkyl and alkoxygroups having from 1 to 3 carbon atoms. Non-limiting representativespecies include: 2-(3,5-bis(chlorocarbonyl)phenoxy)acetic acid,3-(3,5-bis(chlorocarbonyl)phenyl) propanoic acid,2-((1,3-dioxo-1,3-dihydroisobenzofuran-5-yl)oxy)acetic acid,3-(1,3-dioxo-1,3-dihydroisobenzofuran-5-yl)propanoic acid,2-(3-(chlorocarbonyl) phenoxy)acetic acid,3-(3-(chlorocarbonyl)phenyl)propanoic acid,3-((3,5bis(chlorocarbonyl)phenyl) sulfonyl) propanoic acid,3-((3-(chlorocarbonyl)phenyl)sulfonyl)propanoic acid,3-((1,3-dioxo-1,3-dihydroisobenzofuran-5-yl)sulfonyl)propanoic acid,3-((1,3-dioxo-1,3-dihydroisobenzofuran-5-yl)amino) propanoic acid,3-((1,3-dioxo-1,3-dihydroisobenzofuran-5-yl)(ethyl)amino)propanoic acid,3-((3,5-bis(chlorocarbonyl) phenyl)amino) propanoic acid,3-((3,5-bis(chlorocarbonyl) phenyl)(ethyl)amino) propanoic acid,4-(4-(chlorocarbonyl)phenyl)-4-oxobutanoic acid,4-(3,5-bis(chlorocarbonyl)phenyl)-4-oxobutanoic acid,4-(1,3-dioxo-1,3-dihydroisobenzofuran-5-yl)-4-oxobutanoic acid,2-(3,5-bis(chlorocarbonyl) phenyl)acetic acid,2-(2,4-bis(chlorocarbonyl)phenoxy) acetic acid,4-((3,5-bis(chlorocarbonyl) phenyl)amino)-4-oxobutanoic acid,2-((3,5-bis(chloro carbonyl)phenyl)amino)acetic acid,2-(N-(3,5-bis(chlorocarbonyl)phenyl)acetamido)acetic acid,2,2′((3,5-bis(chlorocarbonyl)phenylazanediyl) diacetic acid,N-[(1,3-dihydro-1,3-dioxo-5-isobenzofuranyl)carbonyl]-glycine,4-[[(1,3-dihydro-1,3-dioxo-5-isobenzofuranyl)carbonyl]amino]-benzoicacid, 1,3-dihydro-1,3-dioxo-4-isobenzofuran propanoic acid,5-[[(1,3-dihydro-1,3-dioxo-5-isobenzofuranyl)carbonyl]amino]-1,3-benzenedicarboxylicacid and 3-[(1,3-dihydro-1,3-dioxo-5-isobenzofuranyl)sulfonyl]-benzoicacid.

Another embodiment is represented by Formula III.

wherein the carboxylic acid group may be located meta, para or orthoupon the phenyl ring.

Representative examples where the hydrocarbon moiety is an aliphaticgroup are represented by Formula IV.

wherein X is a halogen (preferably chlorine) and n is an integer from 1to 20, preferably 2 to 10. Representative species include:4-(chlorocarbonyl) butanoic acid, 5-(chlorocarbonyl) pentanoic acid,6-(chlorocarbonyl) hexanoic acid, 7-(chlorocarbonyl) heptanoic acid,8-(chlorocarbonyl) octanoic acid, 9-(chlorocarbonyl) nonanoic acid,10-(chlorocarbonyl) decanoic acid, 11-chloro-11-oxoundecanoic acid,12-chloro-12-oxododecanoic acid, 3-(chlorocarbonyl)cyclobutanecarboxylicacid, 3-(chlorocarbonyl)cyclopentane carboxylic acid,2,4-bis(chlorocarbonyl)cyclopentane carboxylic acid,3,5-bis(chlorocarbonyl) cyclohexanecarboxylic acid, and4-(chlorocarbonyl) cyclohexanecarboxylic acid. While the acyl halide andcarboxylic acid groups are shown in terminal positions, one or both maybe located at alternative positions along the aliphatic chain. While notshown in Formula (IV), the acid-containing monomer may includeadditional carboxylic acid and acyl halide groups.

Representative examples of acid-containing monomers include at least oneanhydride group and at least one carboxylic acid groups include:3,5-bis(((butoxycarbonyl)oxy)carbonyl)benzoic acid,1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid,3-(((butoxycarbonyl)oxy)carbonyl)benzoic acid, and4-(((butoxycarbonyl)oxy)carbonyl)benzoic acid.

The upper concentration range of acid-containing monomer may be limitedby its solubility within the non-polar solution and is dependent uponthe concentration of the tri-hydrocarbyl phosphate compound, i.e. thetri-hydrocarbyl phosphate compound is believed to serve as a solubilizerfor the acid-containing monomer within the non-polar solvent. In mostembodiments, the upper concentration limit is less than 1 wt %. In oneset of embodiments, the acid-containing monomer is provided in thenon-polar solution at concentration of at least 0.01 wt %, 0.02 wt %,0.03 wt %, 0.04 wt%, 0.05 wt %, 0.06 wt %, 0.07 wt %, 0.08 wt %, 0.1 wt%or even 0.13wt % while remaining soluble in solution. In another set ofembodiments, the non-polar solution comprises from 0.01 to 1 wt %, 0.02to 1 wt %, 0.04 to 1 wt % or 0.05 to 1 wt % of the acid-containingmonomer. The inclusion of the acid-containing monomer during interfacialpolymerization between the polyfunctional amine and acyl halide monomersresults in a membrane having improved performance. And, unlike posthydrolysis reactions that may occur on the surface of the thin-filmpolyamide layer, the inclusion of the acid-containing monomer duringinterfacial polymerization is believed to result in a polymer structurethat is beneficially modified throughout the thin-film layer.

Once brought into contact with one another, the polyfunctional acylhalide and polyfunctional amine monomers react at their surfaceinterface to form a polyamide layer or film. This layer, often referredto as a polyamide “discriminating layer” or “thin film layer,” providesthe composite membrane with its principal means for separating solute(e.g. salts) from solvent (e.g. aqueous feed). The reaction time of thepolyfunctional acyl halide and the polyfunctional amine monomer may beless than one second but contact times typically range from about 1 to60 seconds. The removal of the excess solvent can be achieved by rinsingthe membrane with water and then drying at elevated temperatures, e.g.from about 40° C. to about 120° C., although air drying at ambienttemperatures may be used. However, for purposes of the presentinvention, the membrane is preferably not permitted to dry and is simplyrinsed (e.g. dipped) with water and optionally stored in a wet state.Once formed, the polyamide layer is exposed to nitrous acid. A varietyof techniques is described in U.S. Pat. No. 4,888,116 and which areincorporated herein by reference. It is believed that the nitrous acidreacts with the residual primary amine groups present in the polyamidediscrimination layer to form diazonium salt groups. At least a portionof these diazonium salt groups hydrolyze to form phenol groups or azocrosslinks via diazo-coupling. Although the aqueous solution may includenitrous acid, it preferably includes reagents that form nitrous acid insitu, e.g. an alkali metal nitrite in an acid solution or nitrosylsulfuric acid. Because nitrous acid is volatile and subject todecomposition, it is preferably formed by reaction of an alkali metalnitrite in an acidic solution in contact with the polyamidediscriminating layer. Generally, if the pH of the aqueous solution isless than about 7, (preferably less than about 5), an alkali metalnitrite will react to liberate nitrous acid. Sodium nitrite reacted withhydrochloric or sulfuric acid in an aqueous solution is especiallypreferred for formation of nitrous acid. The aqueous solution mayfurther include wetting agents or surfactants. The concentration of thenitrous acid in the aqueous solution is preferably from 0.01 to 1 wt %.Generally, the nitrous acid is more soluble at 5° than at 20° C. andsomewhat higher concentrations of nitrous acid are operable at lowertemperatures. Higher concentrations are operable so long as the membraneis not deleteriously affected and the solutions can be handled safely.In general, concentrations of nitrous acid higher than about one-half(0.5) percent are not preferred because of difficulties in handlingthese solutions. Preferably, the nitrous acid is present at aconcentration of about 0.1 weight percent or less because of its limitedsolubility at atmospheric pressure. The temperature at which themembrane is contacted can vary over a wide range. Inasmuch as thenitrous acid is not particularly stable, it is generally desirable touse contact temperatures in the range from about 0° to about 30° C.,with temperatures in the range from 0° to about 20° C. being preferred.Temperatures higher than this range can increase the need forventilation or super-atmospheric pressure above the treating solution.Temperatures below the preferred range generally result in reducedreaction and diffusion rates.

The reaction between the nitrous acid and the primary amine groupsoccurs relatively quickly once the nitrous acid has diffused into themembrane. The time required for diffusion and the desired reaction tooccur will depend upon the concentration of nitrous acid, anypre-wetting of the membrane, the concentration of primary amine groupspresent and the temperature at which contact occurs. Contact times mayvary from a few minutes to a few days. The optimum reaction time can bereadily determined empirically for a particular membrane and treatment.

One preferred application technique involves passing the aqueous nitrousacid solution over the surface of the membrane in a continuous stream.This allows the use of relatively low concentrations of nitrous acid.When the nitrous acid is depleted from the treating medium, it can bereplenished and the medium recycled to the membrane surface foradditional treatment. Batch treatments are also operable. The specifictechnique for applying aqueous nitrous acid is not particularly limitedand includes spraying, film coating, rolling, or through the use of adip tank among other application techniques. Once treated the membranemay be washed with water and stored either wet or dry prior to use. ForRO and NF applications, membranes treated with nitrous acid preferablyhave a NaCl rejection of at least 2% when tested using an aqueous NaClsolution (250 ppm) at 25° C. and 70 psi.

A representative reaction scheme illustrating the treatment of thepolyamide with nitrous acid is provided below.

The thin film polyamide layer of the subject membranes preferably has anazo content (—N═N—) of less than 0.80, 0.75%, 0.70% and in someembodiments less than 0.65%. In other embodiments, the thin film layerhas from 0.30% to 0.80% or more preferably 0.40% to 0.75% azo content.As used herein, the term “azo content” refers to the amount of diazoniumcoupling (diazo coupling and azo coupling) resulting from two aromaticcompounds that are coupled by a —N═N— group. Diazonium cations which aregenerated by treatment of aromatic amine with nitrous acid or strongermineral acid, may participate in an electrophilic aromatic substitutionreaction as an electrophile. The electrophilic reaction center is theterminal nitrogen of the —N═N⁺ group in a coupling reactions withanilines or phenols. As a result, two aromatic compounds are coupled by—N═N— group. The resultant reaction is called diazonium coupling inwhich a representative reaction scheme is illustrated above. Pyrolysisgas chromatography is the preferred technique for measure the azocontent of the thin film polyamide layer. By way of example, the azocontent of the thin film polyamide layer may be determined by using aFrontier Lab 2020iD pyrolyzer mounted on an Agilent 6890GC with a 30m×0.32 mm 10 μm Moisieve 5 Å PLOT from Agilent connected to a thermalconductivity detector (TCD). Ammonium dichromate (NH₄Cr₂O₇) is used as acalibration standard which upon thermal degradation at 600° C. producedone mole of N₂. A standard calibration solution is made by dissolvingapproximately 10 mg of NH₄Cr₂O₇ in 10 mL of water. To make thecalibration solutions, 2, 3, 4, and 5 μL of the standard solution aredeposited into the sample cups and linear least squares routine is usedto develop a response factor. Pyrolysis on the standards is performed at600° C. for 6 seconds. The backing and polysulfone layers of thecomposite polyamide membrane are removed (delaminated) and the resultingmembrane is weighed into sample cups in the range of 200 μg andpyrolyzed at 550° C. for 6 seconds using the single shot mode, Thesample weight was used to determine the weight percent of N₂ releasedfrom the membranes which corresponds to the weight percent of azo(—N═N—) linkages in the membranes, For the gas chromatographyconditions, the columns are maintained at a constant flow of 1.8 mL/minof helium with the injector having a split ratio of 30:1 at 280° C. Theoven is programmed from 38° C. for 1 minute and 38 to 200° C. at 25° C.per minute. The TCD is maintained at 150° C. with a reference flow of 14mL/min and combined flow of 7 mL/min. This methodology was used todetermine the azo content of the samples described in the Examplesection.

In a preferred embodiment, the thin film polyamide layer ischaracterized by having a dissociated carboxylate content of at least0.18, 0.20, 0.3, 0.4 and in some embodiments at least 0.45 moles/kg ofpolyamide at pH 9.5 as measured by a Rutherford Backscattering (RBS)measurement technique. In other embodiments, the thin film layer has adissociated carboxylate content of less than 0.50 moles/kg, e.g. 0.18 to0.50 moles/kg. By way of specific example of the RBS technique, samplesmembranes (1 inch×6 inch) are boiled for 30 minutes in deionized water(800 mL), then placed in a 50/50 w/w solution of methanol and water (800mL) to soak overnight. Next, 1 inch×1 inch size sample of thesemembranes are immersed in a 20 mL 1×10⁻⁴ M AgNO₃ solution with pHadjusted to 9.5 for 30 minutes. Vessels containing silver ions arewrapped in tape and to limit light exposure. After soaking with thesilver ion solution, the unbound silver is removed by soaking themembranes in 2 clean 20 mL aliquots of dry methanol for 5 minutes each.Finally, the membranes are allowed to dry in a nitrogen atmosphere for aminimum of 30 minutes. Membrane samples are mounted on a thermally andelectrically conductive double sided tape, which was in turn mounted toa silicon wafer acting as a heat sink. The tape is preferably ChromericsThermattach T410 or a 3M copper tape. RBS measurements are obtained witha Van de Graff accelerator (High Voltage Engineering Corp., Burlington,Mass.); A 2 MeV He⁺ room temperature beam with a diameter of 3 mm at anincident angle of 22.5°, exit angle of 52.5°, scattering angle of 150°,and 40 nanoamps (nAmps) beam current. Membrane samples are mounted ontoa movable sample stage which is continually moved during measurements.This movement allows ion fluence to remain under 3×10¹⁴ He⁺/cm².Analysis of the spectra obtained from RBS is carried out using SIMNRA®,a commercially available simulation program. A description of its use toderive the elemental composition from RBS analysis of RO/NF membranes isdescribed by; Coronell, et. al. J. of Membrane Sci. 2006, 282, 71-81 andEnvironmental Science & Technology 2008, 42(14), 5260-5266. Data can beobtained using the SIMNRA® simulation program to fit a two layer system,a thick polysulfone layer beneath a thin polyamide layer, and fitting athree-layer system (polysulfone, polyamide, and surface coating) can usethe same approach. The atom fraction composition of the two layers(polysulfone before adding the polyamide layer, and the surface of finalTFC polyamide layer) is measured first by XPS to provide bounds to thefit values. As XPS cannot measure hydrogen, an H/C ratio from theproposed molecular formulas of the polymers were used, 0.667 forpolysulfone and a range of 0.60-0.67 was used for polyamide. Althoughthe polyamides titrated with silver nitrate only introduces a smallamount of silver, the scattering cross section for silver issubstantially higher than the other low atomic number elements (C, H, N,O, S) and the size of the peak is disproportionately large to the othersdespite being present at much lower concentration thus providing goodsensitivity. The concentration of silver is determined using the twolayer modeling approach in SIMNRA® by fixing the composition of thepolysulfone and fitting the silver peak while maintaining a narrowwindow of composition for the polyamide layer (layer 2, rangespredetermined using XPS). From the simulation, a molar concentration forthe elements in the polyamide layer (carbon, hydrogen, nitrogen, oxygenand silver) is determined. The silver concentration is a directreflection of the carboxylate molar concentration available for bindingsilver at the pH of the testing conditions. The moles of carboxylicacids groups per unit area of membrane is indicative of the number ofinteractions seen by a species passing through the membrane, and alarger number will thus favorably impact salt passage. This value may becalculated by multiplying the measured carboxylate content by a measuredthickness and by the polyamide density. Alternatively, the carboxylatenumber per unit area of membrane (moles/m2) may be determined moredirectly by methods that measure the total complexed metal within aknown area. Approaches using both Uranyl acetate and toluidine blue Odye are described in: Tiraferri, et. al., Journal of Membrane Science,2012, 389, 499-508. An approach to determine the complexed cation(sodium or potassium) content in membranes by polymer ashing isdescribed in (Wei Xie, et al., Polymer, Volume 53, Issue 7, 22 March2012, Pages 1581-1592). A preferred method to determine the dissocatedcarboxylate number at pH 9.5 per unit area of membrane for a thin filmpolyamide membrane is as follows. A membrane sample is boiled for 30minutes in deionized water, then placed in a 50 wt % solution ofmethanol in water to soak overnight. Next, the membrane sample isimmersed in a 1×10⁻⁴ M AgNO₃ solution with pH adjusted to 9.5 with NaOHfor 30 minutes. After soaking in the silver ion solution, the unboundsilver is removed by soaking the membranes twice in dry methanol for 30minutes. The amount of silver per unit area is preferably determined byashing, as described by Wei, and redissolving for measurement by ICP.Preferably, the dissocated carboxylate number at pH 9.5 per square meterof membrane is greater than 6×10⁻⁵, 8×10⁻⁵, 1×10⁻⁴, 1.2×10⁻⁴, 1.5×10⁻⁴,2×10⁻⁴, or even 3×10⁻⁴ moles/m^(2.)

In another embodiment of the invention, the thin film polyamide layerpreferably has a ratio of carboxylic acid functional groups to amidegroups (—COOH:(—C(O)NH—)) of equal to or greater than 0.13, 0.15 or 0.16as determined by ATR IR. A preferred method for determining this ratiois conducted by first isolating the polyamide layer from the poroussupport by first delaminating from the backing sheet. The delaminatedmembrane is then immersed in a solvent suitable to dissolve the poroussupport (e.g. dimethyl formamide). After dissolving the porous support,the insoluble polyamide is collected by filtration, washed 4 timesdimethylformamide, 3 times with DI water, and 3 times with methanol thendried in a vacuum oven at 50 C. for 20 hours. Infrared spectra ofdelaminated polyamide layer may be acquired with a Perkin Elmer SpectrumOne FT-IR and Universal ATR Sampling Accessory at a nominal resolutionof 4 cm⁻¹ and 16 scans (approximate acquisition time of 90 seconds). TheUniversal ATR Sampling Accessory is preferably equipped with a singlebounce diamond/ZnSe crystal. The carboxylic acid peak height wasmeasured at 1706 cm⁻¹ with a single-point baseline at 1765 cm⁻¹. Theamide peak height was measured at 1656 cm⁻¹ with a single-point baselineat 1765 cm⁻¹. This method was used to analyze the samples described inthe Example section.

In another embodiment of the invention, the thin film polyamide layerpreferably has a ratio of phenol amine functional groups to m-phenylenediamine groups of at least 0,13, 0.18, 0.19, or even 0.20. A preferredrange is from 0.13 to 0.30. A preferred pyrolysis methodology wasconducted using a Frontier Lab 2020iD pyrolyzer mounted on an Agilent6890 GC according to the Frontier Lab manufacturer conditions. Peak areadetection was made using a flame ionization detector (FID). Membranesamples were weighed into Frontier Labs silica lined stainless steelcups using a Mettler E20 micro-balance capable of measuring to 0.001 mg.Sample weight targets were 200 μg+/−50 μg. The pyrolysis was conductedby dropping the sample cup into the oven set at 650° C. for 6 seconds insingle shot mode. Separation was performed using a 30M×0.25 mm id with a1 μm 5% phenyl methyl silicone internal phase column from Varian(FactorFour VF-5MS CP8946). Gas chromatograph conditions were thefollowing: Agilent 6890 GC (SN:CN10605069), with a 30M×0.25 mm, 1 μm 5%dimethyl polysiloxane phase (Varian FactorFour VF-5MS CP8946). Injectionport 320° C., Detector port: 320° C., Split injector flow ratio of 50:1,GC Oven conditions: 40° C. to 110° C. at 5° C. per min., 110° C. to 320°C. at 20° C./min, 320° C. for 10 min; Helium carrier gas with constantflow of 0.6 mL/min (17 cm/sec) providing a back pressure of 8.0 psi.Detector gas flows: H₂ at 40 mL/min, air at 400 mL/min, He makeup at 30mL/min.

When both a carboxylic acid monomer and a tri-hydrocarbyl phosphate areincluded in the preparation of the thin film polyamide layer, theresulting polymer is believed to be more flexible (i.e. more open) ascompared with control membranes. When these type of membranes are posttreated, the probability of resulting diazotized amine and amino phenolgroups (resulting from hydrolysis of diazotized amine) being present inclose enough proximity to facilitate azo coupling are much lower thanpost treated control membranes. As a consequence, membranes madeaccording to one embodiment of the present invention have lower azocontent and a higher amino phenol to mPD ratio as compared with controlmembranes. In order for the carboxylic acid groups (resulted from theincorporation of carboxylic acid monomer in the membrane) to contributeto Donnan exclusion (i.e. reducing NaCl passage), the openness of thestructure of the polymer structure is believed to be essential. Areduced azo content and corresponding higher amino phenol contentindicate that the openness of the polymer structure is maintained afterdiazotization. And as a result, the subject membranes provided reducedNaCl passage and in some cases, increased flux.

The thin film polyamide layer may optionally include hygroscopicpolymers upon at least a portion of its surface. Such polymers includepolymeric surfactants, polyacrylic acid, polyvinyl acetate, polyalkyleneoxide compounds, poly(oxazoline) compounds, polyacrylamides and relatedreaction products as generally described in U.S. Pat. No. 6,280,853;U.S. Pat. No. 7,815,987; U.S. Pat. No. 7,918,349 and U.S. Pat. No.7,905,361. In some embodiments, such polymers may be blended and/orreacted and may be coated or otherwise applied to the polyamide membranefrom a common solution, or applied sequentially.

Many embodiments of the invention have been described and in someinstances certain embodiments, selections, ranges, constituents, orother features have been characterized as being “preferred.”Characterizations of “preferred” features should in no way beinterpreted as deeming such features as being required, essential orcritical to the invention.

EXAMPLES Example 1

Sample membranes were prepared using a pilot scale membranemanufacturing line. Polysulfone supports were casts from 16.5 wt %solutions in dimethylformamide (DMF) and subsequently soaked in anaqueous solution meta-phenylene diamine (mPD). The resulting support wasthen pulled through a reaction table at constant speed while a thin,uniform layer of a non-polar coating solution was applied. The non-polarcoating solution included a isoparaffinic solvent (ISOPAR L) andtrimesoyl acid chloride (TMC). In selected samples the non-polar coatingsolution further included tri butyl phosphate (TBP) provided in a 1:1.5stoichiometric ratio with TMC and in other samples, both TBP and 0.03wt/vol % 1-carboxy-3,5-bis(chlorocarbonyl)benzoic acid (mh-TMC). Excessnon-polar solution was removed and the resulting composite membrane waspassed through water rinse tanks and drying ovens. Sample membranesheets were then either (i) stored in deionized water until testing; or(ii) “post treated” by being soaked for approximately 15 minutes in asolution at 5-15° C. prepared by combining 0.05% w/v NaNO₂ and 0.1 w/v %HCl and thereafter rinsed and stored in deionized water at roomtemperature until testing. Testing was conducted using a 2000 ppm NaClsolution at room temperature, pH 8 and 150 psi. Mean average flux isexpressed in GFD. As shown by the test results summarized in Table 3,post-treatment of samples produced using a tri-hydrocarbyl compound andcarboxylic acid monomer had an unexpected improvement in flux overcomparable control membranes.

TABLE 1 (component mixture used to prepare sample thin film polyamidelayers) Series Series Monomer content Series 1-1 Series 1-2 Series 1-31-4 1-5 mPD (wt/vol %) 2.5 3.5 3.5 3.5 4.5 TMC (wt/vol %)* 0.15 0.150.19 0.23 0.15 *except in series “e” and “f” where the TMC content wasreduced by 0.03 wt/vol % and 0.03 wt/vol % of mh-TMC was included.

TABLE 2 Sample Series Overview 1-(1, 2, 3, 4, 5, 6) a Control (made viaa method consistent with U.S. Pat. No. 4,277,344) 1-(1, 2, 3, 4, 5, 6) bControl w/ “post treatment” (made via a method consistent with U.S. Pat.No. 4,888,116) 1-(1, 2, 3, 4, 5, 6) c Control w/ TBP in 1:1.5stoichiometric ratio with TMC (made via a method consistent with U.S.Pat. No. 68782780 1-(1, 2, 3, 4, 5, 6) d Control w/ TBP in 1:1.5stoichiometric ratio with TMC and “post treatment” (no basis in priorart) 1-(1, 2, 3, 4, 5, 6) e Control w/ TBP in 1:1.5 stoichiometric ratiowith TMC, 0.03 wt/ vol % mh-TMC (made via a method consistent withWO2013/048765) 1-(1, 2, 3, 4, 5, 6) f Control w/ TBP in 1:1.5stoichiometric ratio with TMC, 0.03 wt/ vol % mh-TMC and “posttreatment” (no basis in prior art)

TABLE 3 Avg Flux NaCl Dis. carboxylate Amino (GFD) Passage (%) contentAzo content COOH/ phenol/ Sample (SD) (SD) (moles/kg) (%) amide mPDratio 1-1a 11.8 (0.27)  1.8 (0.36) 0.11 0.12 1-1b* 11.7 (0.69) 2.19(0.92) 0.13 1.13 0.14 0.07 1-1c 52.1 (1.39) 1.50 (0.24) 0.06 0.13 1-1d*68.1 (2.55) 1.77 (0.13) 0.07 0.83 0.10 0.08 1-1e 51.1 (0.79) 1.63 (0.11)0.32 0.13 1-1f* 74.8 (0.66) 1.47 (0.11) 0.19 0.46 0.16 0.22 1-2a 20.7(0.36) 0.74 (0.08) 0.15 0.13 1-2b* 24.0 (0.36) 0.95 (0.08) 0.16 0.990.13 0.10 1-2c 36.2 (0.72) 0.63 (0.02) 0.10 0.10 1-2d* 48.3 (1.63) 0.73(0.01) 0.16 0.88 0.09 0.06 1-2e 26.3 (0.80) 2.28 (0.75) 0.38 0.14 1-2f*40.4 (0.93) 1.52 (0.12) 0.34 0.54 0.16 0.18 1-3a 13.9 (0.44) 0.97 (0.07)0.14 0.13 1-3b* 14.9 (0.56) 1.11 (0.03) 0.21 0.97 0.11 0.08 1-3c 40.7(1.39) 0.75 (0.13) 0.13 0.09 1-3d* 52.7 (1.92) 0.92 (0.02) 0.16 0.870.09 0.06 1-3e 40.2 (1.36) 0.37 (0.03) 0.31 0.15 1-3f* 57.4 (0.70) 0.60(0.07) 0.32 0.75 0.15 0.19 1-4a 11.9 (1.16) 1.18 (0.03) 0.18 0.10 1-4b*11.9 (1.57) 1.21 (0.17) 0.21 1.01 0.12 0.06 1-4c 40.3 (0.84) 0.94 (0.08)0.08 0.08 1-4d* 52.6 (1.94) 1.22 (0.09) 0.06 0.94 0.10 0.08 1-4e 45.5(0.24) 0.52 (0.03) 0.31 0.14 1-4f* 59.4 (0.86) 0.73 (0.08) 0.32 0.550.14 0.19 1-5a 22.6 (0.54) 0.65 (0.01) 0.10 0.11 1-5b* 27.6 (0.14) 0.63(0.02) 0.11 1.07 0.12 0.12 1-5c 23.9 (0.49) 0.57 (0.06) 0.04 0.08 1-5d*32.6 (0.39) 0.51 (0.01) 0.07 0.83 0.09 0.13 1-5e 20.1 (0.24) 0.36 (0.01)0.17 0.13 1-5f* 29.6 (0.56) 0.36 (0.02) 0.20 0.69 0.17 0.23 Samplessubjected to post-treatment with nitrous acid are designed with anasterisk (*).

Example 2

Sample membranes were prepared and tested in the same manner as Example1 except that mh-TMC was replaced with varying quantities of monohydrolyzed isophthaloyl chloride (mh-IPC), and for all runs mPD was keptconstant at 3.5 wt % and total acid chloride was kept constant at 0.2wt/vol % . Results are summarized in Table 4.

TABLE 4 mh IPC Avg Flux NaCl Dis. carboxylate Amino conc (GFD) Passagecontent Azo content COOH/ phenol/ Sample (wt/vol) % (SD) (%) (moles/kg)(%) amide mPD ratio 2-1a 0 35.14 0.51% 0.12 0.106 2-1b* 0 35.55 0.70%0.12 0.3 0.126 0.21 2-2a 0.01 38.43 0.60% 0.14 0.111 2-2b* 0.01 41.490.53% 0.16 0.28 0.099 0.21 2-3a 0.02 37.41 0.57% 0.19 0.127 2-3b* 0.0237.83 0.48% 0.19 0.32 0.113 0.18 2-4a 0.03 35.00 0.62% 0.17 0.12 2-4b*0.03 34.76 0.43% 0.23 0.38 0.112 0.16 2-5a 0.04 33.51 0.78% 0.22 0.1622-5b* 0.04 33.20 0.40% 0.26 0.31 0.139 0.2 2-6a 0.05 30.61 0.61% 0.250.133 2-6b 0.05 32.61 0.40% 0.25 0.35 0.144 0.17

1. A thin film composite polyamide membrane comprising a porous supportand a thin film polyamide layer characterized by possessing: i) an azo(—N═N—) content of from 0.30% to 0.80%, as measured by pyrolysis gaschromatography using ammonium dichromate as a calibration standard andpyrolizing the polyamide layer at 550° C. for 6 seconds: ii) adissociated carboxylate content of at least 0.20 mol/kg as measured byRBS at pH 9.5:and iii) an amino phenol/m-phenylene diamine ratio of atleast 0.15.
 2. (canceled)
 3. The membrane of claim 1 wherein the thinfilm polyamide layer is further characterized by possessing an azocontent of from 0.40% to 0.75%.
 4. The membrane of claim 1 wherein thethin film polyamide layer is further characterized by possessing aCOOH/amide ratio of equal to or greater than 0.14, as measured by ATRIR.
 5. The membrane of claim 1 wherein the thin film polyamide layer isfurther characterized by possessing a COOH/amide ratio of equal to orgreater than 0.15, as measured by ATR IR.
 6. The membrane of claim 1wherein the thin film polyamide layer is further characterized bypossessing a COOH/amide ratio of equal to or greater than 0.16, asmeasured by ATR IR.
 7. (canceled)
 8. The membrane of claim 1 wherein thethin film polyamide layer is further characterized by possessing anamino phenol/m-phenylene diamine ratio of at least 0.18.
 9. The membraneof claim 1 wherein the thin film polyamide layer is furthercharacterized by possessing: i) an azo content of from 0.40% to 0.75%;ii) a dissociated carboxylate content of at least than 0.30 mol/kg; iii)a COOH/amide ratio of equal to or greater than 0.14; and iv) aminophenol/m-phenylene diamine ratio of at least 0.18.